In general, an aluminum flake pigment has been widely employed as a luster pigment blended into a paint composition or an ink composition in various fields of bodies of automobiles, motorcycles, bicycles and other vehicles and parts thereof, optical instruments such as cameras and video cameras, OA appliances, sporting goods, containers for food, beverages, cosmetics etc., audio products such as radio cassette recorders and CD players and domestic appliances such as cleaners, telephone sets and televisions or in the field of gravure printing, offset printing, screen printing etc.
While various types of aluminum flake pigments have heretofore been developed in various fields, an aluminum flake pigment having an average particle diameter in the range of 18 to 30 μm and an average thickness in the range of 0.5 to 1.5 μm or the like is frequently employed, as disclosed in Japanese Patent Laying-Open No. 10-1625, for example.
However, characteristics required to the aluminum flake pigment in these fields are improved year after year, and an aluminum flake pigment capable of obtaining a printing layer presenting classiness having excellent metallic luster, fine-grainedness and silvery plating-like luminance is demanded particularly in relation to gravure printing, offset printing, screen printing etc. Also in the field of paint compositions, an aluminum flake pigment capable of obtaining a film presenting classiness having plating-like luminance is strongly required.
In general, an aluminum evaporated flake pigment obtained by flakily pulverizing an evaporated aluminum thin film prepared by evaporating aluminum on a resin film with a thickness in the range of 0.02 to 0.06 μm and thereafter dissolving/removing this film has been used for satisfying such requirement.
However, this method is so inferior in productivity that the performance and the cost are unbalanced, and the working range thereof has been limited to narrow applications. When an aluminum flake pigment such as evaporated powder having a small thickness is to be prepared by conventional wet pulverization or grinding through a ball mill or the like (hereinafter simply referred to as grinding), the pigment is parted by pulverization before the thickness thereof is sufficiently reduced, and hence it has been impossible to obtain a sufficient plating-like film or ink by employing this aluminum flake pigment.